1. Field of the Invention
The invention relates to a hydraulic lifting device used in car maintenance and repair, more particularly to an improved hydraulic lifting device which can be used when removing or installing gearboxes and which can also be used to lift car engines.
2. Description of the Related Art
Presently, the removal and/or installation of a chassis part which is relatively heavy to handle, such as a gearbox, has to be undertaken when conducting car chassis maintenance and repair. In order to remove or install such parts, it is sometimes necessary to raise the car body to a level which is approximately equal to a man's height, thereby facilitating access to the car chassis.
When removing a gearbox from the car body, a special jack or hydraulic lifting device is first secured to the base of the gearbox. The gearbox is loosened from the car body, and the jack or hydraulic lifting device is then operated so as to remove the gearbox from the car body.
FIG. 1 is an illustration of a conventional hydraulic jack which is used when installing or removing a gearbox from the car body. The hydraulic jack includes a mobile base (11) which has caster units (12) provided thereon. A double acting hydraulic cylinder (13) is mounted vertically on the mobile base (11). A mounting plate (14) is provided on a top end of the hydraulic cylinder (13). Adjusting means (15, 16) are installed so as to permit adjustments in the inclination of the mounting plate (14). Finally, clamping units (17) are provided on the mounting plate (14) so as to secure the gearbox thereon.
The following are the main drawbacks of the above-described hydraulic jack:
1. Note that when the hydraulic cylinder (13) is in a fully retracted position after the gearbox has been removed from the oar body, the mounting plate (14) is disposed at a relatively high level with respect to the ground. The center of gravity due to the combined weight of the hydraulic jack and the gearbox is relatively high, thereby increasing the instability of the hydraulic jack. Movement of the hydraulic jack should therefore be conducted with utmost care in order to prevent toppling of the same.
2. Since the mounting plate (14) is disposed at a relatively high level with respect to the ground even when the hydraulic cylinder (13) is in a fully retracted position after the gearbox has been removed from the car body, another tool must be used or a relatively large force must be exerted in order to move the gearbox from the mounting plate (14) to a workbench and to move the gearbox back to the mounting plate (14) after the gearbox has been repaired. Such movements are therefore inconvenient to conduct.
3. The length of the hydraulic jack when in a fully extended position is approximately 1.9 meters. Movement of a piston of the hydraulic cylinder (13) from a fully retracted position to a fully extended position takes a relatively long time because a relatively long distance, approximately meter, is involved. Furthermore, movement of the hydraulic jack from the fully retracted position to the fully extended position is inconvenient to accomplish because a hand lever of the same should be operated about 100 times in order to achieve such a result.
4. A torque is generated whenever the center of gravity of the gearbox is not aligned with the axis of the hydraulic jack. The torque increases the instability of the hydraulic jack and produces friction between the piston and the hydraulic cylinder (13) of the hydraulic jack, thereby affecting the useful life of the same.
5. The double acting hydraulic cylinder (13) requires high precision machining and is therefore difficult and expensive to construct.
Note that it is sometimes necessary to remove a car engine from the car body when conducting engine maintenance and repair. The above-described hydraulic jack cannot be used to lift car engines. Instead, a specially designed engine hoisting device is used for this purpose.
Referring to FIG. 2, a conventional engine hoisting device is shown to comprise a mobile base (2) which has caster units provided thereon. The front end (21) of the mobile base (2) is extendible. The width of the rear end (22) of the mobile base (2) can be adjusted. An upright prop (23) is secured on the mobile base (2). A support arm (24) has one end hinged to the top of the upright prop (23). A chain hook (25) is provided on the other end of the support arm (24) and is used for hanging a car engine thereon. A hand-operated hydraulic cylinder (26) is provided between the upright prop (23) and the support arm (24). The hydraulic cylinder (26) is operated so as to raise or lower the chain hook (25) relative to the mobile base (2).
Note that the above-disclosed engine hoisting device is only used for lifting car engines and cannot be used when installing or removing a gearbox from the car body.